Effects of layer thickness and binder saturation level parameters on 3D printing process

Various parameters, such as binder properties, printing layer thickness, powder size, and binder saturation level, have effects on the strength and surface finish of the three-dimensional printing (3D printing) process. The objective of this research is to study the effects of two parameters of layer thickness and binder saturation level on mechanical strength, integrity, surface quality, and dimensional accuracy in the 3D printing process. Various specimens include tensile and flexural test specimens and individual network structure specimens are made by the 3D printing process under different layer thicknesses and binder saturation by use of ZCorp.'s ZP102 powder and Zb56 binder. Two printing layer thicknesses, 0.1 and 0.087 mm, are evaluated at 90% and 125% binder saturation levels. Experimental findings show that under the same layer thickness, increment of binder saturation level from 90% to 125% would result in an increase of tensile and flexural strengths of the specimens and decrease of dimensional accuracy and surface uniformity of specimens. On the other hand, under the same binder saturation conditions, increase in layer thickness from 0.087 to 0.1 mm would decrease tensile strength and increase flexural strength. Also, it gives better uniformity on the surface.     

聚乳酸/羟基磷灰石复合材料激光选区烧结工艺优化与性能研究

以生物可降解材料聚乳酸（PLA）和生物骨基质的主要无机成分羟基磷灰石（HA）为研究对象。为获得复合材料激光选区烧结(SLS)制件的最佳成形参数，首先对纯PLA的SLS工艺进行了优化，发现最优的激光能量密度范围为0.040~0.075 J/mm2，且制得的纯PLA试样的拉伸强度均超过23 MPa，最高可达27.28 MPa。为研究HA含量对PLA/HA复合材料微观结构与力学性能的影响，以激光能量密度为0.040 J/mm2（激光功率12 W,扫描速度1 500 mm/s）对不同HA含量的PLA/HA复合材料进行了成形。实验结果表明，当HA质量分数为10%时，PLA/HA复合材料的力学性能和微观形貌最优。水接触角测试显示材料的接触角从69.52°降至57.96°，表明材料的亲水性能得到了改善。     

纳米Al2O3填充LDPE/POM复合材料的力学和摩擦性能研究

采用挤出混合与注塑成型制备出不同含量的纳米Al2O3填充LDPE/POM复合材料,并进行力学和摩擦磨损性能实验。结果表明,随着纳米Al2O3的增加,LDPE/POM复合材料的缺口冲击性能先提高后降低,其中添加8%纳米Al2O3后复合材料的缺口冲击强度提高了近3倍;添加Al2O3纳米粒子后增加了复合材料的摩擦因数,但对耐磨性影响不大。由于纳米Al2O3作为刚性粒子可以提高材料的硬度,因此复合材料仍表现出良好的耐磨性;然而纳米粒子在摩擦表面富集,产生了犁沟现象,因此提高了材料的摩擦因数。     

Fabrication of Carbon Nanotubes and Rare Earth Pr Reinforced AZ91 Composites by Powder Metallurgy

It can be known from a large number of research results that improving the dispersibility of CNTs can effectively opti-mize the mechanical properties of the corresponding metal matrix composites.However,the crucial issue of increas-ing the bonding of CNTs and the matrix is still unsolved.In this paper,a novel method was developed to increase interfacial bonding strength by coating titanium oxide(TiO2)on the surface of CNTs.The rare earth Pr and TiO2@CNTs-reinforced AZ91 matrix composites were successfully fabricated by powder metallurgy.Hot press sintering and hot extrusion of the milled powder was performed.After hot extrusion,the influence of TiO2@CNTs on the microstruc-ture and mechanical properties of the composites were investigated.The results showed that the coating process can improve the distribution of CNTs in Mg alloy.The CNTs refined the grains of the matrix,and the CNTs were presented throughout the extrusion direction.When the TiO2@CNTs content was 1.0 wt.％,the yield strength(YS),ultimate ten-sile strength(UTS),and elongation of the alloy attained maximum values.The values were improved by 23.5％,82.1％,and 40.0％,respectively,when compared with the AZ91 alloy.Good interfacial bonding was achieved,which resulted in an effective tensile loading transfer at the interface.CNTs carried the tensile stress and were observed on the tensile fracture.     

Correlation of the tribological behaviors with the mechanical properties of poly-ether-ether-ketones (PEEKs) with different molecular weights and their fiber filled composites

The tribological behaviors of three poly-ether-ether-ketones (PEEKs) with different molecular weights and their SCF (short carbon fiber)/graphite/PTFE (polytetrafluoroethylene) filled composites were examined using a block-on-ring apparatus under dry sliding conditions. Tensile tests, hardness measurements and dynamic mechanical thermal analysis (DMTA) of the PEEK based materials were also performed. The tribological behaviors of PEEK based materials were correlated with their mechanical properties and the tribological mechanisms were discussed based on scanning electron microscope (SEM) inspections of worn surfaces and wear debris. Under a low apparent pressure, a high material ductility seems to reduce the wear rate of pure PEEK through alleviating the microcutting effect exerted by the protruding regions of the counterpart. Under a high pressure, however, a high stiffness seems to improve the wear resistance of pure PEEK by reducing the plastic flow occurring in the PEEK surface layer. After incorporating SCF/graphite/PTFE fillers, the wear rate of PEEK was decreased significantly. Thinning and cracking of SCF are supposed to be the important factors determining the tribological behaviors of the composites.     

A comparison of ultrasound and computed tomography in evaluating the mechanical properties of trabecular bone

This study compared ultrasound parameters and bone mineral density (BMD) in the assessment of the mechanical properties of trabecular bone. The BMD of bovine tibial trabecular bone specimens was measured by CT scanning each specimen in all three orthogonal directions. Similarly, ultrasound velocity and attenuation measurements were also made in these directions. Specimens were then divided into three groups for mechanical testing. the ultimate strength, Young's modulus and energy absorption were measured for each specimen. It was found that BMD was independent of trabecular orientation while ultrasound velocity and attenuation values were significantly higher in the superior/inferior (SI) direction corresponding to the load bearing axis at stance. All mechanical properties were also significantly higher in the SI direction. The linear correlation demonstrated that ultrasound parameters, particularly ultrasound velocity, were better than BMD as predictors of compressive mechanical properties     

Microstructural and mechanical properties of nanometric magnesium oxide particulate-reinforced aluminum matrix composites produced by powder metallurgy method

In this research, aluminum alloy (A356.1) matrix composites reinforced with 1.5, 2.5 and 5 Vol.% nanoscale MgO particles were fabricated via powder metallurgy method. Pure atomized aluminum powder with an average particle size of 1μm and MgO particulate with an average particle size between 60 to 80 nm were used. The specimens were pressed by Cold Isostatic Press machine (CIP), and were subsequently sintered at various sintering temperatures, viz. 575, 600 and 625°C. Optimum amount of reinforcement and sintering temperature were determined by evaluating the density, microstructure and mechanical properties of composites. The composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Hardness and compression tests were carried out in order to identify mechanical properties. Reinforcing the Al matrix alloy with MgO particles improved the hardness and compressive strength of the alloy to a maximum value of 44 BHN and 288 MPa, respectively. The most improved compressive strength was obtained with the specimen including 2.5% of MgO sintered at 625°C. According to the experiments, a sintering temperature of 625°C showed better results than other temperatures. A good distribution of the dispersed MgO particulates in the matrix alloy was achieved.     

尼龙6／铜复合粉末选区激光烧结工艺参数优化及力学性能研究

制备了不同铜粉含量（质量分数）的尼龙6机械混合复合粉末,对复合粉末进行激光烧结,利用扫描电镜对烧结件的形貌进行了表征,通过正交试验优化工艺参数,并研究了铜粉含量对烧结件力学性能的影响。结果表明,铜粉与尼龙表面黏结良好,铜粉均匀分布在尼龙基体中;随着铜粉含量增加,烧结件抗弯强度、抗拉强度显著提高,冲击强度逐渐降低;铜粉含量为50％时,烧结试样抗拉强度为43．28MPa,抗弯强度为77．66MPa,硬度为112HRL,分别比纯尼龙6提高了10．04％、59．27％和39．29％。     

基于电场驱动熔融喷射聚合物基复合材料高分辨率3D打印

针对当前聚合物基复合材料（Polymer matrix composites，PMC）成型存在打印分辨率低、打印材料受限、成型结构较为简单、工序复杂等方面的不足和局限性，尤其是还面临难以实现宏/微结构跨尺度高效制造的挑战性难题，提出一种基于电场驱动熔融喷射PMC高分辨率3D打印新工艺。阐述了基于电场驱动熔融喷射PMC高分辨率3D打印的基本原理和工艺流程。通过试验，揭示了主要工艺参数（碳填料含量、施加电压、螺杆转速、打印速度、加热温度等）对于打印件分辨率（精度）和质量的影响及其规律。利用自主搭建的试验平台，并结合试验优化的工艺参数和提出的两种打印模式，实现了多层石墨烯/聚乳酸（Polylactic acid，PLA）和多壁碳纳米管/PLA复合材料微尺度三维网格、多层石墨烯/PLA大高宽比薄壁圆环、多壁碳纳米管/PLA复合材料柔性导电网格以及其他聚合物复合材料3D结构典型工程案例的制造。研究结果表明，提出的电场驱动熔融喷射3D打印能实现高分辨聚合物基复合材料成型（使用内径300 μm喷嘴，实现了分辨率为40 μm的PMC特征结构制造），而且还具有大面积宏/微结构跨尺度集成制造的优势。     

碳纤维/玻璃纤维/石墨协同改性PTFE复合材料力学性能

通过机械混合、冷压和烧结成型制备了碳纤维、玻璃纤维和石墨填充协同改性聚四氟乙烯(PTFE)复合材料。对比分析了不同样品的拉伸、冲击和压缩等力学性能。结果表明:玻纤和碳纤维使复合材料冲击强度下降;玻纤使复合材料拉伸强度下降,碳纤维则使复合材料拉伸强度稍有增强;玻纤和碳纤维均使复合材料压缩强度增加,但碳纤维的增强效果更为明显;石墨、玻纤和碳纤维协同增强PTFE复合材料的拉伸强度较高,弹性模量较大,断裂伸长率较高,抗压缩性能明显提高,且材料拉伸时呈塑性断裂,是综合力学性能较好的高性能润滑密封材料。     

Tribological characteristics of a microtextured polymer fabricated via an additive manufacturing process

With the growing interest in 3D printing, many studies are being conducted to replace conventional manufacturing processes. In terms of mechanical applications, however, research on the tribological characteristics of 3D printing components has not been sufficiently conducted. This study investigated the influences of surface texturing and roughness on 3D printed specimens. Specimens with and without surface texture were printed using a 3D printer, and their frictional behavior was compared. The friction coefficient of the textured specimen was smaller than that of the untextured specimen. Contact analysis was conducted to evaluate the mechanism. The analysis suggested that the real contact area of the untextured specimen was similar to that of the textured specimen during the initial stage. However, the wear of asperities during the friction test increased the real contact area of the untextured specimen. Surface roughness was verified to influence the untextured specimen more significantly than the textured specimen in terms of tribological behavior.

     

FDM制备晶格点阵结构体的一种卡扣式打印方法的研究

熔融沉积技术（Fused deposition modeling,FDM）打印晶格点阵结构时,存在着打印件机械性能差、支撑材料难去除的问题。针对这些问题,本文将晶格结构体分解成数个二维模型,通过FDM进行分体打印然后利用卡扣配合重新组装。利用这种分体打印工艺深入探索了BCC、BCC-Z、F2CC和F2CC-Z这4种典型结构类型的晶格体结构的表面形貌和机械性能,并与传统一体式打印进行对比。发现该卡扣式分体方法实现了打印物体表面质量的改善、打印时间和打印材料的节省以及抗压性能的提升。该研究为实现3D打印制备晶格结构体提供了一种途径,并为选择合适的晶格类型提供了参考。     

Mechanical properties of bio-absorbable PLA/PGA fiber-reinforced composites

This study investigated important mechanical properties, the flexural strength and flexural modulus, of polyglycolic acid (PGA) fiber-reinforced polylactic acid (PLA) composites fabricated by melt-mixing. The flexural strength and flexural modulus were estimated using three-point bending tests conducted at 37°C. Both the flexural strength and flexural modulus were increased by PGA fiber reinforcement. Viscoelastic properties were also investigated using dynamic mechanical analysis (DMA) under tensile loading. Results show that PGA fiber, which acts as the nucleate agent of PLA, restrains the molecular chains of PLA. That restraint reduces deformation at the same stress condition, thereby improving the PLA flexural properties.     

Development of composite porous scaffolds based on poly(lactide-co-glycolide)/nano-hydroxyapatite via selective laser sintering

Poly(lactide-co-glycolide) (PLGA)/nano-hydroxyapatite (nano-HAP) composite porous scaffolds with well-controlled pore architectures as well as high exposure of the bioactive ceramics to the scaffold surface were fabricated via selective laser sintering. Neat PLGA and the composite of PLGA/nano-HAP were used to obtain suitable process parameters. The effects of nano-HAP content on the microstructure and mechanical properties were investigated. The testing results showed that the compressive strength and modulus of the scaffolds were highly enhanced when the nano-HAP content reached from 0 to 20 wt%, while the mechanical properties experienced a sharp dropped with the nano-HAP content further increased. This might be due to the large reduction in polymer which decreased the interface bond strength between particles. It suggests that the introduction of nano-HAP as a reinforcing phase can improve the mechanical properties of the polymer porous scaffolds. The novel developed scaffolds may serve as a three-dimensional bone substrate in tissue engineering.     

Structural and mechanical properties of nanocrystalline titanium and 316LVM steel processed by hydrostatic extrusion

The aim of the present study was to examine the potential of hydrostatic extrusion for the fabrication of high‐strength materials for medical applications. The materials examined were 316LVM steel and technically pure titanium. The microstructures and mechanical properties of the materials before and after hydrostatic extrusion were analysed. It was found that the hydrostatic extrusion process resulted in a substantial refinement of the material microstructures. The refinement of the microstructure was accompanied by an improvement of the mechanical properties, such as the microhardness and yield stress.     

连续纤维自增强复合材料3D打印及其回收性能研究

连续纤维增强复合材料3D打印工艺的出现,为复合材料构件低成本快速制造提供了一种新方法,为了充分利用3D打印连续纤维增强热塑性复合材料成形快,易成形复杂零部件的特点,结合自增强复合材料具有良好界面结合性,可循环利用的优势,分析了自增强复合材料3D打印技术研究的发展现状,提出一种利用过冷熔体成形连续纤维自增强复合材料的3D打印方法,设计了基于过冷的自增强复合材料熔融挤出打印喷头,采用聚苯硫醚(Polyphenylene sulfid,PPS)纤维与PPS树脂作为自增强复合材料原材料,探究自增强复合材料成形打印温度窗口、复合材料力学性能、微观界面结合性,以及对连续纤维自增强复合材料完全可回收性能研究分析。     

FEM of residual stress and surface displacement of a single shot in high repetition laser shock peening on biodegradable magnesium implant

Laser shock peening (LSP) is one of the prominent surface processing techniques to improve the mechanical characteristics by inducing compressive residual stress on the specimen surface. Generally, LSP is performed using high energy, low repetition pulsed laser. Recently, High repetition laser shock peening (HRLSP) on biodegradable magnesium alloys has been reported. Increased speed and reduced operating costs are the key highlights of HRLSP. This work is aimed towards understanding of the residual stress profile beneath the specimen surface, where a Finite element method (FEM) has been proposed to show the ability of a tightly focussed nanosecond laser pulse for peening magnesium. The depth of maximum compressive residual stress of 48 MPa at 28 mm beneath surface was the result of the simulation. Also the Von Misses stress was analytically found to be 31.5 MPa, which is similar to the value from FEM at 30 MPa. Furthermore, the plastic displacement of FEM at 4.02 µm compares reasonably well with the experimental result at 3.698 µm, thereby validating the Finite element model. If increase in CRS can be created by single shot of laser pulse, it can be concluded that the same can be done beneath the entire magnesium surface using appropriate scanning protocols.

     

仿生多材料复合增强骨软骨支架的制造及性能研究

针对关节面上大面积骨软骨缺损修复过程中软骨形态恢复和力学环境恢复困难的问题,设计并制造一种新型聚乙二醇(Polyethylene glycol, PEG)/ 聚乳酸(Polylactide, PLA)/ β-磷酸三钙(β-Tricalcium phosphate, β-TCP)仿生多材料复合增强骨软骨支架。基于CT扫描数据重建的羊膝关节模型上进行仿生多材料骨软骨支架的结构设计,包括多孔定制结构和固定桩及仿生结构;以光固化成形技术与真空灌注工艺相结合制造了的多材料复合增强骨软骨支架,确定灌注温度220℃,真空度–0.08～–0.10 Pa。形貌观测表明真空灌注法能使PLA完全充满整个次级管道,力学试验发现复合材料支架的压缩强度(21.25 MPa ± 1.15 MPa)是单管道多孔生物陶瓷支架(9.76 MPa± 0.64 MPa)的2.17倍, PLA固定桩的剪切强度(16.24 MPa±1.85 MPa)是陶瓷固定桩(0.87 MPa±0.14 MPa)的18.7倍。因此,复合PLA的骨软骨支架具有显著的力学增强和固定能力,有望为大面积骨软骨缺损的修复提供新的治疗手段。     

再生碳纤维回收利用及其增材制造复合材料性能评价

为实现碳纤维增强树脂基复合材料废弃物高效、高质、环境友好型回收与再生碳纤维高值再利用,提出了热活化氧化物半导体回收碳纤维与再生碳纤维增强复合材料(rCFRP)增材再制造的工艺方法。通过电磁顺磁共振与红外光谱测试分析了回收原理,基于单因素实验研究了树脂基体分解率的影响因素以及显著因素对再生碳纤维结构、性能的作用规律,探究了再生碳纤维增强聚乳酸复合材料(rCF/PLA)的力学性能及其产品应用。结果表明,回收过程无液相产物,气相产物主要为CO₂、H₂O;树脂基体分解率与温度、时间呈正相关,O₂浓度及流量作用不显著,树脂基体分解率可达97.1%且再生碳纤维表面无积碳产生。再生碳纤维表面氧化与石墨结构刻蚀程度随温度升高而增加,在一定温度下,合理的处理时间可减小其表面氧化与石墨结构刻蚀程度。再生碳纤维的单丝拉伸性能与温度、时间呈正相关,其单丝拉伸性能可保持原碳纤维的99%以上。与聚乳酸相比,rCF/PLA的抗拉强度提高了7.47%,抗弯强度与模量分别提高了12.29%与52.4%;与原碳纤维增强聚乳酸复合材料相比,rCF/PLA的抗...     

FDM 3D打印聚醚醚酮零件摩擦磨损特性研究

为研究3D打印各向异性对摩擦性能的影响,通过熔融沉积成型(FDM)制备了0°、45°、90°3种打印角度的聚醚醚酮(PEEK)试样,研究3种不同打印角度及载荷变化对PEEK试样摩擦学性能及磨损机制的影响。利用MFT-5000摩擦磨损试验机对PEEK材料进行室温水润滑下的往复滑动摩擦试验,用超景深显微镜观察磨损后表面形貌。试验结果表明：不同载荷下3种打印角度试样的摩擦因数由大到小依次为0°试样、90°试样、45°试样,磨损率由大到小依次为90°试样、45°试样、0°试样;随着载荷的增大,3种不同打印角度试样的摩擦因数均呈现下降趋势,磨损率则呈现上升趋势;PEEK磨损机制是黏着磨损以及疲劳磨损引起的表层脱落。